A rubber crawler, which is mounted on a motor vehicle such as an earth-moving vehicle, as shown in FIGS. 7 and 8, presents an endless belt shape. The illustrated rubber crawler 101 is basically formed of a crawler body 103 that is made of rubber. The rubber crawler 101 is entrained around a drive roller 105 and an idler roller 107. A plurality of take-up rollers 109 is disposed at an inner peripheral side of the rubber crawler 101.
A number of cores 111 are embedded in the crawler body 103 with predetermined spacing along a longitudinal direction of the rubber crawler. The cores 111 extend in a direction orthogonal to the rubber crawler longitudinal direction (i.e., a widthwise direction of the rubber crawler) and are disposed parallel with one another. A number of engagement holes 113 (sprocket holes) are formed in the crawler body and respectively disposed between two adjacent cores. Teeth of the drive roller (sprocket) engage with the engagement holes 113.
Projections 111A of the cores 111 protrude from the rubber crawler inner peripheral surface.
Cord layers are provided at posterior positions (at an outer peripheral side) on each side in the rubber crawler widthwise direction. Each cord layer is comprised of a plurality of steel cords C, each of which extends along the rubber crawler longitudinal direction and which are embedded parallel with one another.
A plurality of lugs 115 are regularly provided at predetermined pitches in the rubber crawler longitudinal direction, each lug extending from the outer peripheral surface of the rubber crawler 101. All the lugs are integrally formed with crawler body 103.
Such a conventional type rubber crawler generally has a shape or structure which is symmetrical in relation to the sprocket holes (a rubber crawler longitudinal center line). However, recently, a rubber crawler, which has an asymmetrical structure, has appeared. It is resulted from the fact that forming positions of sprocket holes are respectively shifted from widthwise direction center positions to one side due to an increase in crawler width based on the tendency of vehicles to become large. A thickness (rubber thickness) of a left side portion of a crawler body and a thickness (rubber thickness) of a right side portion of the crawler body are the same as in the conventional symmetrical type rubber crawler as described above.
In such an asymmetrical type rubber crawler, a body portion and lugs, which are located at a shorter side, with regard to a length between a sprocket hole center and a side end face, of a crawler body, are damaged more easily than those located at a longer side of the crawler body. In other words, there is a concern that a rubber-made crawler body portion located at a weakened side might be unilaterally damaged or worn out. It is considered that this is because the areas of left and right portions of a rubber crawler, to which portions loads are applied when the rubber crawler is being used, are different from each other, and accordingly, the surface pressure differs between the left and right portions.
With respect to this problem, a convenient solution is conceivable in which ground contacting areas at left and right portions of lugs are made approximately equal. However, difficulties are experienced in designing a rubber crawler having such a structure.
Thus, it is generally said that asymmetrical type rubber crawlers have a short life.